| Andi Kleen | 2aae950 | 2007-07-21 17:10:01 +0200 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2006 Andi Kleen, SUSE Labs. |
| 3 | * Subject to the GNU Public License, v.2 |
| 4 | * |
| 5 | * Fast user context implementation of getcpu() |
| 6 | */ |
| 7 | |
| 8 | #include <linux/kernel.h> |
| 9 | #include <linux/getcpu.h> |
| 10 | #include <linux/jiffies.h> |
| 11 | #include <linux/time.h> |
| 12 | #include <asm/vsyscall.h> |
| 13 | #include <asm/vgtod.h> |
| 14 | #include "vextern.h" |
| 15 | |
| 16 | long __vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache) |
| 17 | { |
| 18 | unsigned int dummy, p; |
| 19 | unsigned long j = 0; |
| 20 | |
| 21 | /* Fast cache - only recompute value once per jiffies and avoid |
| 22 | relatively costly rdtscp/cpuid otherwise. |
| 23 | This works because the scheduler usually keeps the process |
| 24 | on the same CPU and this syscall doesn't guarantee its |
| 25 | results anyways. |
| 26 | We do this here because otherwise user space would do it on |
| 27 | its own in a likely inferior way (no access to jiffies). |
| 28 | If you don't like it pass NULL. */ |
| 29 | if (tcache && tcache->blob[0] == (j = *vdso_jiffies)) { |
| 30 | p = tcache->blob[1]; |
| 31 | } else if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) { |
| 32 | /* Load per CPU data from RDTSCP */ |
| 33 | rdtscp(dummy, dummy, p); |
| 34 | } else { |
| 35 | /* Load per CPU data from GDT */ |
| 36 | asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG)); |
| 37 | } |
| 38 | if (tcache) { |
| 39 | tcache->blob[0] = j; |
| 40 | tcache->blob[1] = p; |
| 41 | } |
| 42 | if (cpu) |
| 43 | *cpu = p & 0xfff; |
| 44 | if (node) |
| 45 | *node = p >> 12; |
| 46 | return 0; |
| 47 | } |
| 48 | |
| 49 | long getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache) |
| 50 | __attribute__((weak, alias("__vdso_getcpu"))); |